Nickel-based semifinished product having a cube recrystallization texture, corresponding method of production and use

ABSTRACT

A nickel-based semifinished product has a cube recrystallization texture and the semifinished product can e.g. be used as a support for physicochemical coatings having a highly microstructured orientation. Such supports are e.g. suitable as substrates for ceramic coatings such as are used in the field of high-temperature supraconductivity. In this case, the product is used in supraconducting magnets, transformers, motors, tomographs and supraconducting current paths. There is provided a nickel-based semifinished product that has improved performance characteristics when used as a support for physicochemical coatings having a highly microstructured orientation. Especially the semifinished product should have a higher-grade, thermally more stable cube texture while substantially preventing the formation of grain boundary grooving. For this purpose, Ag in the microalloy range is added to the material of the semifinished product, the added Ag being not more than 0.3 atomic percent. The inventive semifinished product is e.g. suitable as a support for physicochemical coatings having a highly microstructured orientation.

BACKGROUND OF THE INVENTION

The invention relates to a semi-finished product on a nickel basis with a cubic recrystallization texture and a method for its production.

The semi-finished product can be used, for example, as a base for physical, chemical coatings with a high-grade microstructural alignment. Such bases are suitable, for example, as substrates for ceramic coatings, as used in the field of high-temperature superconduction. In this case, such bases are used in superconducting magnets, transformers, motors, tomographs or superconducting current paths.

It is known that polycrystalline metals with a cubic, face-centered lattice, such as nickel, copper and aluminum, after a prior high-grade cold working by rolling, can develop a pronounced texture with a cubic layer during the subsequent recrystallization (G. Wasserman: Texturen metallischer Werkstoffe (Textures of Metallic Materials), Springer, Berlin, 1939). Metallic strip textured in this way, especially nickel strips, are also used as a base for metallic coatings, ceramic buffer layers and ceramic superconducting layers (U.S. Pat. No. 5,741,377). The suitability of such metal strip as a substrate material depends primarily on the achievable degree of texturing and on the stability of the texture in the region of the temperatures, at which the collecting processes are carried out.

Semi-finished products for the preparation of high-temperature superconductors are already known and consist of Ni—Cr, Ni—Cr—V, Ni—Cu and similar alloys (U.S. Pat. Nos. 5,964,966 and 6,106,615).

Nickel alloys with molybdenum and tungsten are also known for these purposes (DE 100 05 861 C1).

The known semi-finished products have the following disadvantages:

-   -   after a cold working process and recrystallization annealing,         nickel has a great tendency to form a coarse grain structure,         which is disadvantageous for achieving the high-great cubic         texture;     -   during the recrystallization heat treatment, especially at         higher temperatures (800° to 1150° C.) cold worked nickel strip         has a great tendency to form rifts at grain boundaries;     -   the rifts at grain boundaries may represent an appreciable         impediment to the formation of a high-grade, biaxial cubic         texture; and     -   substrate material with rifts at grain boundaries is less         suitable as a base for epitaxial layer depositions, for example,         for buffer layers and superconducting layers.

SUMMARY OF THE INVENTION

It is an object of the invention to develop a semi-finished product on a nickel basis, which has improved use properties for use as a base for physical, chemical coatings with a high-grade microstructural alignment. In particular, the semi-finished product is to have a higher grade, thermally more stable cubic texture and the formation of rifts at grain boundaries is to be largely avoided. The development of a method for the preparation of this semi-finished product is included in this task.

This objective is accomplished owing to the fact that the material of the semi-finished product contains an addition of silver in the micro-alloying range, the addition of silver not exceeding 0.3 atom percent.

In accordance with an appropriate development of the invention, the nickel alloy may contain molybdenum and/or tungsten as alloying elements.

There may be a cubic textured nickel oxide layer with a textured portion of more than 90% on the inventive semi-finished product. This layer is suitable as a diffusion barrier and enables qualitatively high-grade coatings to be produced, especially under oxidizing conditions.

The formation of a high-grade cubic texture is favored and the thermal formation of grain boundary rifts on the nickel surface of the semi-finished product is hindered by the inventive addition of silver. Moreover, the addition of silver enables a high-grade nickel oxide layer, which is provided with a cubic texture, to be grown on the semi-finished product.

A feature of the inventive method of preparing the semi-finished product is that, initially, by melt metallurgical or powder metallurgical means, including mechanical alloying, a semi-finished product is prepared, which consists of technically pure nickel or a nickel alloy, in which a silver addition in the micro-alloying range is contained in an amount of less than 0.3 atom percent. Subsequently, the semi-finished product is processed by means of hot working, followed by a high-grade cold working involving a more than 80% reduction in thickness to a strip or flat wire. Finally, this semi-finished product is subjected to a recrystallizing annealing in order to achieve a cubic texture.

Subsequently or during the recrystallizing annealing, the semi-finished product, so prepared, may be heat treated pursuant to the invention in an oxidizing atmosphere for the purpose of growing a cubic textured nickel oxide layer.

Pursuant to the invention, the semi-finished product may be used as a base for physical, chemical coatings with a high-grade microstructural alignment, especially for the production of wire-shaped or strip-shaped, high-temperature superconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph depicting sharp recrystallization cubic texture; and

FIGS. 2(a) and 2(b) are photographs rotated 45° with respect to the texture of the nickel strip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is explained in greater detail below, by means of examples, which show the successful testing of the invention. A portion of the test results is documented in FIGS. 1 and 2 and in Table 1 below.

Example 1

Technically pure nickel, which has a degree of purity of 99.9 atom percent and has been alloyed with 0.01 atom percent of silver, is cast in a mold. The ingot is rolled at 1000° C. into the square dimension (22×22 mm2), annealed to homogenize it and quenched. Subsequently, the square material is reworked with chip removal in order to obtain a defect-free surface for the subsequent cold working by rolling. The cold working is carried out with a reduction in thickness by rolling of more than 80%, in this case, 99.6%. The resulting nickel strip has a thickness of 80 mm and a high-grade, rolled texture. It is subsequently subjected to a 30-minute annealing treatment at 550° C. in a non-oxidizing gas atmosphere.

The result is an exceptionally sharp recrystallization cubic texture, as is evident from the photograph of FIG. 1. The proportion of crystallites with a cubic state is 98% and the proportion of small angle grain boundaries also is 98%. The half value width of the intensity of the (111) pole in X-ray diffraction is FWHM=4.4°.

Example 2

Technically pure nickel, which has a degree of purity of 99.9 atom percent and has been alloyed with 0.01 atom percent of silver, is melted in a vacuum induction furnace and poured into a mold. The ingot is rolled at 1000° C. to the square dimension (22×22 mm2), annealed to homogenize it and quenched. Subsequently, the square material is reworked with chip removal in order to obtain a defect-free surface for the subsequent cold working by rolling. The cold working is carried out with a reduction in thickness by rolling of more than 80%, in this case, 99.6%. The resulting nickel strip has a thickness of 80 mm and a high-grade, rolled texture. It is subsequently subjected to a 30-minute annealing treatment at 550° C. in a reducing gas atmosphere.

The result is an almost complete recrystallization cubic texture. Subsequently, the strip is exposed to a 5-minute oxidation in pure oxygen gas at 1150° C.

The resulting nickel oxide layer has a cubic texture, 97% of the grains having the cubic state. This texture is rotated through 45° with respect to the texture of the nickel strip (see FIGS. 2(a) and 2(b)). The FWHM value of the (111) pole is of the order of 6.2°.

Example 3

Technically pure nickel, which has been alloyed with 0.01 atom percent of silver, is melted and cast in a mold. The ingot is rolled at 1000C into the square dimension (22×22 mm2), annealed to homogenize it and quenched. Subsequently, the square material is reworked with chip removal in order to obtain a defect-free surface for the subsequent cold working by rolling. The cold working is carried out with a reduction in thickness by rolling of 85%. The resulting nickel strip has a thickness of 3 mm and is subsequently subjected to a 30-minute annealing treatment at 850° C. for recrystallization. After that, the surface is cleaned and the strip is worked further cold to a thickness of 80 mm. Finally, it is annealed at 850° C. for 45 minutes in a reducing atmosphere in order to produce the cubic texture.

Example 4

Technically pure nickel, with the addition of 4.0 atom percent of tungsten powder and 0.1 atom percent of silver powder, is processed by powder metallurgical means. After compression, tempering and hot working, a rod material (12×12 mm2) is obtained. The surface is reworked with chip removal, in order to obtain a defect-free surface for the following cold working by rolling. Starting from dimensions of 10×10 mm2, the cold rolling is carried out until the finished product has a thickness of 80 mm. The edge regions of the strip are severed and discarded. The nickel strip obtained is subsequently subjected to a 30 minute annealing at 550° C. in a reducing atmosphere for the recrystallization. Subsequently, the strip is annealed a second time for 8 minutes at 1100° C. in a reducing atmosphere, in order to obtain a thermally highly stressable cubic state.

With the values of the substrates Nos. 5 and 6, the Table 1 below shows the positive effect of the inventive addition of silver on the FWHM (111) values in comparison with the state of the art (substrates Nos. 1 to 4). TABLE 1 FWHM (111) Value Recrystallized Recrystallized Substrate at 550° C. for 30 minutes at 850° C. for 30 minutes 1 Ni 8.3° — 2 Ni + 0.1 7.4° 7.2° atom % of Mo 3 Ni + 0.1 8.8° 8.6° atom % of W 4 Ni 7.9° 6.8° 5 Ni + 0.95 4.8° 5.1° atom % of Ag 6 Ni + 0.01 4.4° 5.3° atom % of Ag 

1.-6. (canceled)
 7. A semi-finished product on a nickel basis, comprising: a nickel-based material including one of technically pure nickel and a nickel alloy; and silver added to said nickel-based material in a micro-alloying range not exceeding 0.3 atom percent, said semi-finished product having a cubic recrystallization texture.
 8. A semi-finished product according to claim 7, wherein: said nickel-based material is said nickel alloy; and said nickel alloy contains at least one of molybdenum and tungsten as alloying elements.
 9. A semi-finished product according to claim 7, wherein a cubic textured nickel oxide layer with a textured portion of more than 90% is present on said semi-finished product.
 10. A semi-finished product according to claim 8, wherein a cubic textured nickel oxide layer with a textured portion of more than 90% is present on said semi-finished product
 11. A semi-finished product according to claim 7, wherein said semi-finished product serves as a base for chemical coatings, said semi-finished product further comprising a physical chemical coating on said base, said chemical coating having a high-grade microstructural alignment.
 12. A semi-finished product according to claim 111 wherein said base and coating define, at least in part, one of a flat wire high-temperature superconductor and a strip-shaped high-temperature superconductor.
 13. A semi-finished product according to claim 8, wherein said semi-finished product serves as a base for chemical coatings, said semi-finished product further comprising a physical chemical coating on said base, said chemical coating having a high-grade microstructural alignment.
 14. A semi-finished product according to claim 13 wherein said base and coating define, at least in part, one of a flat wire high-temperature superconductor and a strip-shaped high-temperature superconductor.
 15. A semi-finished product according to claim 9, wherein said semi-finished product serves as a base for chemical coatings, said semi-finished product further comprising a physical chemical coating on said base, said chemical coating having a high-grade microstructural alignment.
 16. A semi-finished product according to claim 15 wherein said base and coating define, at least in part, one of a flat wire high-temperature superconductor and a strip-shaped high-temperature superconductor.
 17. A method for the production of a semi-finished product, comprising: adding silver to a nickel-based material in a micro-alloying range which does not exceed 0.3 atom %, said nickel-based material including one of technically pure nickel and a nickel alloy; processing said semi-finished product by hot working; carrying out high-grade cold working of more than an 80% reduction in thickness of said semi-finished product; and subjecting said semi-finished product to a recrystallizing annealing to achieve a substantially cubic texture.
 18. A method according to claim 17, wherein said step of adding includes one of melt metallurgical and powder metallurgical processes.
 19. A method according to claim 17, wherein said step of carrying out high-grade cold working results in forming of said semi-finished product into one of a strip and flat wire.
 20. A method according to claim 17, further comprising heat treating the semi-finished product in an oxidizing atmosphere one of during and after said step of subjecting said semi-finished product to the recrystallizing annealing, for the purpose of growing a cubic textured nickel oxide layer.
 21. A method according to claim 17, further comprising: forming the semi-finished product into a base; and coating said base with a physical chemical coating having a high-grade microstructural alignment.
 22. A method according to claim 21, wherein said step of forming creates a shape of said base suitable for use as at least one of a flat wire high-temperature superconductor and a strip-shaped high-temperature superconductor. 